Frequency-stabilized wave-signal apparatus



Feb. 15, 1949. v AIE. HAYES, JR 2,461,642

FREQUENCY STABILIZED WAVE-SIGNAL. APPARATUS Filed July 5, 1946 INVENTOR, T ALBERT E. HAYES, JR.,

TORNEY.

Patented Feb. 15, 1949 UNlTED? STATE-s:

- :reNsr attics Albert Hayes, .l'rr.', West Hartford; Gonna, 2151-3" signerto Hazeltine Research, Incl, Chicago lll, N

a corporatioh .of Illinois Applicatioll July tn- 1946, Serial -No'. '=681,45 3

' 5 Claims" (Cl. 179 1'71. 5)

This slinven'tion relates. to ciansimproved Lirequencyestabilized-e wave-signal apparatus-.1 and x: more particularly to -suchranzapparatusaincludingz azgeneratorof wave signalsztoiwl'iichds coupled meanseforamplitude modulating-the wave siger 5;- na l-sea Whileathe; inverrtionzis'a'subject toiia wider: range. oflzapplications;3iti-iseespecially:suited for; us'eg-slnsa vacuumetube: :OSGlHQUUIZ-ZfOl!IgGllElflbiIIgi; modulatedzwave signalss fand zwill :be particularly. described irrrconn ectiorr with iapparatus: contain; ing isuch an(oscillators:

Itais i conventional in; radio apparatusfto' utilize asia generator ofi'wave signalsfa va'ccumetub'e os-i' cilla'tor. includin'gzone or :more' tunedioscil-l'atory f ci rcuitspcontaining icither": lumrpe'd ior distrihuted reactancesxfor controllingxthe frequency-"of the oscillator; Several:systemsihaveibeendevised for automatically? controlling the E oscillating irequency,"romexamplesto prevent s1ow'r iriequency 1 changes; thecontrol effect being zprop'ortional t the deviation ofithc frequencyfrom the resonant frequency-:cftan :rauxi'liary. tunedrcircuit'. I It usu'=i allyiaisliconsidered LadvisableivhoWeve T'toi main taimtonly;'zloose icoupling. betweeni the toscillatorfai circuits. and :an i iamplifying or umo'dulating cir 25 cults? in" ordent-itcmavoidideviation iof 1the=:oscilla-"- tiomfreqirency dliemot' to :faiultii turring" or' 'slow' frequency-iidrifting' of 'the' TosCil'latOr :circ'uits; but rathertc changes-r occurringaiinithe amplifyinggor; modulating :circuits. WhGIiit isi-inecessarvtoi o COLlDlGiSlICh "otherr'circuits rather: closely to the circuitszofz the: oscillator. itself, va-rious arrangei-fi' mentstha ve'benzdevelofped for; minimizing devia A tiorriefstheairequency 'ofithe.sigrials generated byi the-ioscill'atorr Onerof :thesearrangementsyfdri' applicationeatot athe ilocali oscillatorcofra super heterodvne receiversincludesifa multi-ele'ment vacuunr'tub'twhaving a Isection': used as an oscil' later and another section used as aim'odulatdnc' three of the elements being used asxa triOd'e local osn-illatomand: the; remaining ielements' iricludiiig theianodet electrode'. being gused .as th'e modulatorii omsfirstndetectoru Oneiibf-thes'eiiremainirig 'el'eisr fa contror electrodeutd iwhi'ch is-applied a woltagersderivedrifor ithevapurposei of automatic 4 5 amplification- :contro1:-' As this? "voltage changes" frumstimevtdltimelirr accordance: witli the avert ageistriengt ofithareceived 'sigiialsthe frequency":- oi lithe-signal?Igeneratedebwthe: local. oscillator tetrds iito :fchauge: This" efieet is diminished by- '50 furnishing a isuitabl'e reactive coupling nfrbm the anodescircuittoffthe first detector to the fre queriey determining circuits of the local oscilla tom- Iri'ztnat-arrangementyhcwevenrnone of-"tlie circuit areltiiitended -to amplitude-modulate:or 55 to cha-nge: in.-any;way;the signal-present in'ihfi v circuits of: -the-.;tri0de -localoscillator itself noris the modulatirigsignal usedto -modiiy or controiiitheeoscillating frequency of .--the local oscillatoi".

toiprevent any: kind of change, in the signal 0f,--the-10ca1' oscillator regardless: of whatvoccurs inzothencircuits coupled to that oscillators- When it isdesiredto producaa wave signal- 0f a :.constant --carrier jsfrequency and .also i to effectamplitude modulation :ofi'this :wave: signal, it: has

become almost K universal .practice-to use. an. ad ditiona-l stageQorstages; ofvtamplification followingvthe circuits -in*which itheiosoillations are gen- .1 erated fi ThesignaL-present imone 10f atheseamphfying stages isethen modulated; and the cou-" pling' between-this; modulator :stage} and :the' 0scillator stage is maintained sufliciently small: to.

prevent anymod-ulationzof signals: in the: oscilla e tor itselfis In certain casessit-has' proved feasible to *apply aud'lo aor 30131161 signals directly "to :the circuitszfot an oscillation generator: to aamplitude modulate the :signal generated therein; but only; very 'low' =-percentagesiofi modulation: are permissible; especially :-with generators of "the higher radioi-frequency oscillations: Ifiit isattempted to modulate the generated signal at all heavily by A means: :coupled': directly .fto such generator; ex cessive deviation: of the carrier frequency tends to occur zduring:modulatiom resulting in" dis'tortiori rofi the .amplit'ude modulated wave "and an 1 excessively: wid'e band bfzt-frequency transmission; Accordingly tit is an object of this? inventiorrto I provideva mew and improved frequency-stabilized waveesig-nal apparatus which substantially: avoids; one. or' more of thefdimitations :of the described prion-arrangements:

It is a further object of this invention'ito' pro-iinew :improved' frequency-staibilized wave-signerapparatusafotgenerating amplitudemodulated" wave signals which i has :an arrangement 5 for: idi-rninishing deviation; OfJithe carrier v frequency/saluting modulation."

In accordancewith'thexinventioh; a ir 'equency'-' stabilized wave=signa1 apparatustcomprises'a "gen efatdl fiibf wavesignals of predetermined carrier frequency and means effective to vary the ampli- The purpose of that arrangement isi-in 3 for utilizing the same modulating signal to control the last-named means substantially to diminish the undesired deviation of the carrier frequency.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, there is shown a schematic circuit diagram illustrating in detail one embodiment of the invention.

Referring to the drawing, there is shown schematically a transmitting apparatus for pro ducing an amplitude-modulated Wave signal of stabilized carrier frequency. The major parts of the apparatus comprise a source it of a moduiating signal such as an audio voltage, an audio ampiifier ii, a generator 52 of wave signals of predetermined carrier frequency, and a utilization means 53 for the output generator i2, the foregoing units being connected in cascade, and also a frequency-modifying circuit is coupled to generator l2.

More specifically, the amplifier indicated gen erally at ii comprises a vacuum tube 29 having a control electrode 2i, which is coupled to source H; by means of an audio transformer 22 with a grounded electrostatic shield, the coupling being eilected through a polarity reversing switch 23. The anodeecathode circuit of amplifier tube 29 includes the conventional self-biasing arrangement 2d and contains the primary of output transformer 25 and a by-pass condenser 25, the circuit being supplied with space current from source indicated 3+. The amplifier ii is coupled through the secondary of transformer 25 to the anode of an electron-discharge means comprising an oscillator tube 3% included in the generator 22, carrier-frequency energy being excluded. from the mnplifier H by carrier-frequency choke 3i. Iube 30 also is supplied with space current from the source 3+, and has a conventional self-biasing arrangement 32 in its control-electrode circuit. Also included in generator i2 is a frequency-determining oscillatory circuit, comprising an inductor 33 and an adjustable condenser 35 coupled to the control electrode or" tube 3i? through the biasing arrangement 32 and to the anode of tube 30 through a blocking condenser 35. A tap on inductor 33 is connected to ground and the cathode of tube 36, thus com- 7 pleting the circuit arrangement of an oscillator of the Hartley type. The utilization means I3 is an antenna circuit, including an'output inductor 36 tuned by a condenser 31 and coupled to antenna 38.

The frequency-modifying means 14 includes an additional electron-discharge means in the form of a tube 40 having an anode All, a cathode t5. and at least one control electrode 43. Connection l5 connects the. anode electrode of oscillator tube 39 to the anode H of tube M3, thus providing a source of space current for tube id. Cathode 42 is connected to ground through a biasing resistor 44 and an audio-frequency bypass condenser 45. Thus the anode-cathode circuit of tube id is coupled to the frequency-detor-mining oscillatory circuit, including inductor Bil and adjustable capacitor 34 through the connection l5 and condenser 35, and through the condenser 45 and the grounded tap on inductor 33.

frequency-modifying unit 14 also includes a phase-splitting means comprising a resistor 4'1 in series with a condenser 58. The point common to resistor ll and condenser 48 is connected to control electrode 43, and'the other terminal of condenser 58 is connected to cathode 42, so that condenser 53 is shunted with the ineherent acpacitance id of the cathode control-electrode circuit of tube 68. The other end of resistor i? is coupled to anode it through a blocking condenser 58. Screen-electrode voltage is supplied to pentode fill! through resistor 51. The control electrode 43 is coupled through a signelfrequency choke 52 to a selected portion 54 of a voltage divider 55, while the portion 54 is grounded to place it in the cathode control-electrode circuit of tube as. .Voltage divider 55 is provided with connections to the source it of audio signals. The signal-frequency choke 52 should have an inductance high enough so that resonance with phase-splitting condenser 48 and the inherent capacitance 09 is avoided, but not so high as to block audio-frequency signals from passing to control electrode 43.

In the operation of the circuits illustrated, a

modulating signal appears at the terminals oi source l8. Thesignal voltage varies in accordance with intelligence desired to be impressed upon the wave signals generated in unit I 2 and, as illustrated, may contain audio-frequency components corresponding to speech or musical signals to be transmitted. Of course, other forms of intelligence, such as the video-image signals used in television systems, also may be used in an apparatus similar to the one illustrated in the drawing; except that circuit modifications would be necessary as is well known to ensure, transmission of the wide band of frequencies required in television systems. The modulating signal is amplified in unit 11 and applied through choke 3! to unit !2, which generates carrierfrequency, wave signals having amplitude variations corresponding to the audio signal amplie fled in unit ii. Modulation of the carrier-frequency signals in unit i2 tends to cause undersired deviation of the carrier frequency. Unit id is included in a'means coupled to unit 12 and effective to modify the carrier frequency of the wave signals generated therein in a manner more fully described hereinafter. Voltage divider 55 by virtue of its connection through choke 52 to control electrode 43 of tube provides for unit M a control arrangement connected to source H1 so as to'utilize the modulating signal in source it] to control the unit M in order substantially to diminish the deviation of the carrier frequency caused my modulation. Thus;-

the carrier frequency is stabilized. Antenna circuit l3 radiates. the amplitude-modulated frequency-stablized' wave signal produced by the described apparatus.

Describing more specifically'the operation of the circuits shown in the drawing, modulating signals from source it! appear in the secondary of transformer 22 and'are applied to control electrode 2l' of tube 20 with apolarity chosen by means of reversing switch 23. Self-biasing arrangement 24 is adjusted in the usual manner to ensure that tube 20 operates on the desired portion of its control-voltage anode current characteristic. The current'in the primary of output transformer 25 varies in accordance with the audio signals applied to control electrode 2|, causing similarly. varying voltages to appear across the secondary of the output transformer.

During operation, the control electrode of oscil- *lator' -=tiibe 3 O draws: current causing a' voltage drop in" the' biasing arrangement 32. 'Currentat the predetern'ziined: carrier-signal frequency circulates} in the oscillatory circuit 33,- 34;dev eIopin accordance"witli the amplifid'modulating sig-' nal appearing in the-secondary of the transformer. tube 30 cause corresponding variations in the amplitude of"thesignal frequerrcy oscillations generatedsin unit l2. Accordingly, amplifier II and a2 part; or tube 30 including its anode electrode constitute means coupled to source and eiiective to vary the amplitude of the wave signals generated by unit l2 in accordance with the modulating signal to produce an amplitude modulated Wave signal. The modulated signal-frequency energy is coupled from inductor 33 into the resonant circuit 36, 31 in the usual manner and thence applied to antenna 38 for radiation.

Variations occurring during modulation in the impedance coupled into the frequency-determining resonant circuit 33, 34 by transformer and a tube 33 tend to cause undesired deviation of the carrier frequency of the wave signals generated by unit 12. To compensate for the variations in impedance coupled into the oscillating circuit in this manner, an additional impedance comprising the impedance between anode 4! and cathode 42 of tube 40 is coupled across tube and hence across the frequency-determining circuit 33, 34 through connection 15, condenser 35, and condenser 45. This additional impedanceis adjusted to have the proper phase relationship to the voltage appearing across circuit 33, 34 by means of the phase-splitting network 41, 48 as modified by the inherent capacitance 49.

The proper adjustment of the impedance of tube is obtained by virtue of the couplingof.

the phase-splitting network to resonant circuit 33, 34 through condensers and 3-5 and through condenser 45 and the tap on inductor 33. This coupling causes signal-frequency current proportional to the carrier-frequency voltage across circuit 33, 34 to flow through the phase-splitting network. By making the resistance of resistor 41 large in proportion to the capacitive reactance of condenser 48, this carrier-frequency current is made to be essentially in phase with the voltage in the resonant circuit. Of course, condensers 50, 35, and 45 all should have sufiiicent capacitance so as to exhibit negligible impedances at the carrier frequency. The in-phase current through the phase-splitting network causes the voltage derived across condenser 48 to be substantially in phase quadrature with the voltage developed by the oscillatory circuit 33, 34, the derived quadrature component being applied to control electrode 43 of tube 40. Proper adjustment of the phase-splitting network makes the Variations in the anode; voltage applied to anode-cathode circuit of tube 40 effective as a l control electrode I 43 :the modulating isignalzeis.

utiiized toccontrol'. the tube 40 1and the-.: entire frequency-modifying: circuit: 1 4. When-t therportion 34- of' rlividerMeand the reversing switcli -fl are r properly adj u'sted, lthe'; frequency-modifying circuit of unit l4 couplesiaicompensatingreactancezint oi the frequency-determiningicircuit 3 3 34 and '--this? diminishes: substantially the undesired de'viation or the carrierirequency caused imamplitude modulation'occurring' in gener'ator ii.

While 'there has beenf described what sis: at present con'sider'ed'ito be the preferredwembodiment' of thisz invention; it 'will be obviousato; those skilled-in the art that various'changes. andimociiiications -maybe: made Ltherein without departing iromthe invention, andfitsis, therefore; aimed-tin the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A frequency-stabilized wave-signal apparatus comprising, a generator of wave signals of predetermined carrier frequency, means efiective to vary the amplitude of the wave signals generated by said generator in accordance with a modulating signal to produce an amplitude-modulated wave signal but tending to cause undesired deviation of the frequency of the wave signals generated by said generator, means coupled to said generator and effective to modify said carrier frequency, and means for utilizing said modulating signal to control said last-named means substantially. to diminish said undesired deviation of said carrier frequency.

2. A frequency-stabilized wave-signal apparatus comprising, a generator of wave signals of predetermined carrier frequency, a source of modulating voltage, means coupled to said source and effective to vary the amplitude of the Wave signals generated by said generator in accordance with said modulating voltage to produce an amplitude-modulated wave signal but tending to cause undesired deviation of the frequency of the wave signals generated by said generator, and means coupled to said generator and having a control arrangement connected to said source for utilizing said modulating voltage to modify said carrier frequency substantially to diminish said undesired deviation thereof.

3. A frequency-stabilized wave-signal apparatus comprising, a generator of wave signals of predetermined carrier frequency, a source of voltage varying in accordance with intelligence desired to be impressed upon said wave signals, means coupled to said source and efiective to vary the amplitude of the wave signals generated by said generator in accordance with said voltage to produce an amplitude-modulated wave signal but tending to cause undesired deviation of the frequency of the wave signals generated by said generator, and means coupled to said generator and having a control arrangement connected to said source for utilizing said voltage to modify said carrier frequency substantially to diminish said undesired deviation thereof.

4. A frequency-stabilized wave-signal apparaenemas trol said second electron-discharge means substantially to diminish said undesired deviation of said carrier frequency.

5. A frequency-stabilized wave-signal apparatus comprising, a generator of Wave signals of predetermined carrier frequency including a first electron-discharge means and an oscillatory circuit coupledthereto for developing a voltage at said carrier frequency, means including at least a part of said first electron-discharge means and eifective to vary the amplitude of the wave signals'generated vby said generator in accordance with a modulating signal to produce an amplitude modulated wave signal but tending to cause undesired deviation of the frequency 01 the wave signals generated by said generator, a second electron-discharge means having an anode-cathode circuit coupled to said oscillatory circuit and having at least onecontrol electrode, phase-splitting means for deriving a component of voltage substantially in phase quadrature with said voltage developed by said oscillatory circuit and plying said component of voltage to one of, s (1 control electrodes; and means coupled to one f said control electrodes for utilizing said modula ing signal to control said second electron-discharge means substantially to diminish said undesired deviation of said carrier frequency.

ALBERT E. HAYES, JR.

' REFERENCES CITED UNITED STATES PATENTS Name Date Tunic}; Sept. 29, 1942 Number 

